Bacterial Vaginosis (BV): This is the most common cause of vaginal discharge and odor in women of reproductive age. The sudden onset of a yellowish brown discharge along with a strong, unpleasant smell is characteristic of BV, which results from an imbalance in the normal vaginal flora.

Trichomoniasis: A sexually transmitted infection caused by the parasite Trichomonas vaginalis, which can lead to a foul-smelling, yellowish green or brown discharge.
Yeast Infection (Candidiasis): Although typically associated with a thick, white discharge, some yeast infections can cause a lighter, brownish discharge, especially if the infection is not fully developed or is mixed with other conditions.
Chlamydia or Gonorrhea: These sexually transmitted infections can cause changes in vaginal discharge, including color and consistency, along with a bad smell.

Pelvic Inflammatory Disease (PID): A serious infection of the female reproductive organs that can cause a range of symptoms, including abnormal vaginal discharge and odor. PID is a medical emergency due to the risk of infertility and other complications.
Cervical Cancer: Although less common, abnormal vaginal discharge can be a symptom of cervical cancer. Regular screening is crucial for early detection.
Foreign Body: The presence of a foreign object in the vagina, such as a forgotten tampon, can cause a strong odor and discharge.

Desquamative Inflammatory Vaginitis (DIV): A rare condition characterized by a purulent, greenish or brown discharge and significant inflammation of the vaginal walls.
Vaginal Cancer: A rare type of cancer that can cause abnormal vaginal discharge among other symptoms.
Atrophic Vaginitis: Thinning and inflammation of the vaginal walls due to a decrease in estrogen levels, which can lead to changes in discharge and odor, though this is less common and typically seen in postmenopausal women.